The present invention relates to data communication and more particularly to wireless asymmetric broadband delivery of data to a plurality of subscriber locations from a common wireless transmission source.
The increasing availability of information in the form of data from various sources has spurred large public demand for broadband data transfer that challenges the capabilities of communication delivery systems. The number of information sources publicly and interactively available via the internet to personal computers, as well as private data network sources, continues to proliferate. Full motion video programming and source material also has rapidly progressed from early television broadcasting and cable distribution networks to a wide variety of distribution arrangements, including direct broadcast satellite television. The number of full motion video sources has expanded in response to increased usage and user demand for a greater range of subject matter content.
To meet user requirements, more robust broadband networks have evolved. For example, Litteral et al. U.S. Pat. No. 5,247,347 discloses a digital video distribution network providing subscribers with access to multiple Video On Demand service providers through the public switched telephone network. The subscriber may transmit ordering information via the public switched telephone network to the independent video information providers. Video programming may be accessed and transmitted to the subscriber directly from a video information provider (VIP) or through a video buffer located at a central office (CO) serving the subscriber. Connectivity between the central office and the subscriber for transmission of video data is provided by an asymmetrical digital subscriber line (ADSL) system. ADSL, which has been standardized by ANSI as T1.413, uses existing unshielded twisted pair copper wires from the telephone company central office to the subscriber""s premises. Equipment at the central office and the subscriber""s premises permits transfer of more high speed digital information signals to the subscriber than in the reverse direction. In the Litteral et al. patent, ADSL interface units at the central office multiplex digital video information with voice information to be transmitted to the subscriber and support two-way transmission between the subscriber""s line and the X.25 packet data network of one or more control channels. A complimentary ADSL interface unit at the subscriber""s premises separates downstream video control signals and voice telephone signals from the line and multiplexes upstream control signals and voice telephone signals onto the line. A similar public switched telephone network multimedia information ADSL delivery system is disclosed, for example, in U.S. Pat. No. 5,528,281 to Grady et al.
A number of patents have proposed various schemes for wireless distribution of information. Hylton et al. U.S. Pat. No. 5,613,191, for example, describes provision of interactive multimedia services including broad band video and audio data and control signals in a multiplexed form to subscriber premises via a communications link from a plurality of information providers. Real time encoders receive video programs and encode the information for those programs into packets of compressed digital data, e.g., in accord with a recognized video compression standard. The head end may also receive previously encoded video program material from other sources, such as a digital server or a digital transmission media. Multiplexers combine digital data for groups of programs into the multiplexed packet data streams. A digital modulator, such as a 64 or 256 QAM modulator, modulates each digitally multiplexed packet data stream for transport in one unique channel. A combined spectrum signal containing these channels is delivered to the subscribers"" premises through suitable multimedia distribution and delivery architecture. The combined spectrum signal channel is connected to a network interface at the subscriber premises where it is up-converted to place the channels into available frequency channels in the UHF range. The unique channel from each digital modulator is fed to an up-converter synthesizer module which performs a frequency hopping spread spectrum technique. The frequency synthesizer uses an input frequency hopping spreading code to determine the particular frequency from within the set of frequencies in the broad frequency band to periodically generate the carrier wave. Frequency hopping codes are input to the frequency synthesizer by a frequency hopping code generator so that the carrier wave is frequency hopped. Each carrier is assigned a different spreading code so that each occupies a different channel during the same time period. The spreading codes are preferably orthogonal to one another so that cross-correlation between the spreading codes is approximately zero. The signals are fed to a suitable miniature subscriber premise antenna for radiation throughout the premises. At the receiver site within the premise a similar antenna receives a signal which is then down-converted and supplied to a wireless signal processor. The wireless signal processor, typically part of an interface module connected by a cable to the down-converter, processes the received wireless signal to select one of the channels. The wireless signal processor effectively acquires a digital multiplexed data stream from the selected channel and supplies that data stream to a digital signal processor. The digital signal processor selects packets of data relating to a selected one of the programs. The digital processing section processes the compressed, digitized data from those packets to produce signals presentable to the subscriber.
While developments such as the systems described above have advanced communication capabilities, limitations remain with respect to meeting the increasing requirements relating to volume of transmission, efficiency and flexibility. Network based systems that deliver data over twisted pair copper wire, even under ADSL communication conditions, are bandwidth limited.
The network data packet transmission modes, such as ATM and the like that have been developed to transport large quantities of video data with high speed and flexibility, contain significant cell overhead that dilutes the proportion of data information payload. ATM networks communicate all information in cells that comprise a well defined and size-limited header area and a user information, or payload, area. CCITT.121/2, the standardized ATM cell format, specifies a 5-byte header field and a 48-byte information or payload field. The header field carries information pertaining to ATM functionality, such as identification of the cells needed for routing purposes. Transfer is asynchronous in the sense that the recurrence of cells that contain information from any particular sender is not necessarily periodic. Each sending device using the ATM network submits a cell for transfer when it has a cell to send, not in accordance with a transmission time slot assigned to the device. The cell overhead is required to enable the ATM switch, or a plurality of ATM switches throughout the network, to rout the transport of cells within the switch and to translate the header information in the cells for appropriate routing of the succeeding ATM cell receiving element.
Wireless communication is less restrictive than the twisted pair wire plant insofar as bandwidth is concerned and does not require the cell overhead of network data transmission arrangements. Thus, cells received over the data network can be stripped of substantial cell overhead for wireless transmission over the subscriber final link. With wireless transmission, however, the signal strength of the radio link is subject to variation with physical conditions and distance. The quality of service of such data transmission thus can be degraded to an unacceptable bit error rate, particularly with transmission at high data rates. Without cognizance of the signal strength and bit error rate over each subscriber radio link, quality of service cannot be accurately assured. Further, present systems do not have efficient means for permitting multiple individual recipients of wireless signals from a given transmission source to presubscribe to different quality of service levels and minimum data throughput rates. For example, subscribers who are to receive real time video data would require a greater throughput at higher bit rate and lower bit error rate than subscribers to whom text is to be downloaded for storage. Other users may require each of these modes at different times but have no avail for subscribing to different quality of service levels on a scheduled or dynamic basis.
The present invention overcomes the above described difficulties in part by providing a wireless, cellular radio link from a base station to a plurality of subscriber stations within a cell reception area. Information data, which may be of textual, video or other format, are communicated asymmetrically, from the standpoint that high bandwidth transmissions occur in the downstream direction to the users while low upstream bandwidth is provided to permit users to request the data or to provide return radio link condition information. Data requests alternatively may be made by the users directly to information providers for delivery of the requested data to the wireless base station location.
An advantage of the present invention is that buffers associated with respective subscribers collect the requested data from the information providers for transmission by the base station in a statistical time division multiplexed (STDM) fashion. Preferably, controlled logical token passing governs a variable-plus-fixed token interval during which data transmission for each buffer is permitted in turn. Users thus can presubscribe to desired data throughput rates.
A further advantage of the present invention is that data fed from the buffers are combined in successive time intervals to form a data stream having a bit rate that can vary from interval to interval. The data stream is output as radio signals from a radio tower, each subscriber being equipped to receive that portion of the stream with which it is identified. The invention thus provides great flexibility in supplying individual user data throughput capacity, as each subscriber data transmission bit rate as well as its transmission time interval can be controllably varied.
A further advantage of the present invention is that variations of data transmission rate and interval for each subscriber can be separately controlled on the basis of both presubscribed levels and current quality of service levels of the radio link. Channel quality and/or bit error rate for each channel may be fed back dynamically from the user for each token interval. The invention thus takes into account quality of service considerations related to the strength of the radio link, which depends on the transmission path operation (e.g., lack of interference, distance, etc.) at any instant, and the contracted minimum data transmission level. The latter has direct bearing on how the token interval length is controlled for the subscriber. Both considerations may impact the data rate within the token interval. The system has the flexibility to change the contracted level on a scheduled or dynamic basis.
Data throughput for each token interval preferably, but not necessarily, occurs through orthogonal frequency division multiplexing (OFDM). Data serially received through the statistical time division multiplexer is output in parallel over separate frequency subcarriers, each modulated in accordance, for example, with quadrature amplitude modulation (QAM). The symbol (data output) rate for each subscriber is set in accordance with the quality of service considerations.